Hlkctbical measukekg appabattts



M. KIRKWOOD.

ELECTRICAL MEASURING APPARATUS.

APPLICATION FILED AUG-9.1918.

Patented Oct. 21,1919.

l i l I l 11:! VEN TOR. Mavleamfifm/twoadk BY f g E A TTORNEY PATENT OFFICE a" con, or user omen, NEW JERSEY, AssiGNon '10 AMERICAN TELE 1 EH NE AND TELEGRAPH CQMPANY, A CORPORATION 013 NEW YORK.

Lame-ea,

To all whom it may concern:

Be it known that T,,MALEAN Kmnwoon,

residing at East Orange, in the county of Essexand State of New Jersey, have in-. vented certain Improvements in Electrical Measuring Apparatus, oil which the following is a specification.

" I T. his invention relates to improvements in electrical measuring apparatus, and more particularly to improvements in apparatus for determining the magnitude of currents induced in a telephone circuit, by power transmissio lines or other fjbl'i 'cal. circuits which extend parallel and in foreign elecclose' proximity to the telephone circuit.

The practice heretofore followed to determine the magnitude of the induced current, consisted in connecting a telephone receiver to the telephone circuit, bridging a shunt across said circuit, and varying the resistance until the receiver gave no audible sound. The shunt used for this purpose consisted in some instances of a varlable resistance, and in other mstances of artificial cable, made-up of reslstances'and capacity.

In using this method with either type of shunt, it has been found difiicult to determine exa'ctl when the point of silence was reached. E xperience has shown that the results obtained from tests made upon the same circuit by two difierent observers some times varied widely. To avoid this diflicult in determining the oint of silence a method was devised whic paring the tone produced in a telephone receiver by the induced current in a telephone circuit with the tone produced in the same receiver by a standard source of alternating current, and varying the current from the said source until it produces the same volume of tone as is produced by the current in the telephone circuit. Experience has shown that this method is productive of greater accuracy than any ordinarily used in measuring the amount of tone or noise induced in a telephone circuit. My invenconsists in com with the seconda ELECTRIGAL MEASURING APPARATUS,

hand side is a circuit diagram of one embodiment of the applicants invention embracing a source of tone and a current controlling and switching mechanism.

lln the drawing, A represents the standard source of alternating current hereinafter referred to as the tone source; B indicates the current controlling and switching apparatus; 0 indicates the telephone circuit in which has been induced an alternating cur- Specification of Letters Patent. P te t e t, 21, 1919 Application filed August a, 1918. Serial No. 249,169.

rent; and D indicates the receiver used in determining when the balance has been attained. The tone source A consists of a vibrator 1 having a primary winding 2 and a secondary. windin 3. The battery 4 is connected to a reversing switch 5. One side of the reversing switch is connected directly to one end of the primary winding 2 and the other side of said switch is connected to the other side of the winding through contact 6 oi switch 7, the function of which will be described later. A condenser 8 is bridged across the contact points of the vibrating element to decrease sparking. .The switch 5 has been inserted in the primary circuit 1n order that the polarity of the connections may be changed after definite intervals of time so as to increase the length of time that the vibrator will run without causing pitting of the buzzer contacts. l

The secondary winding 3 is connected to binding posts '9 and 9 having the current limiting resistances R R and R inserted between the ends of the winding and the binding posts, resistance It, being bridged across and the resistances R and R bemg in series with said winding. The buzzer is designed to have a wave form that will create a tone in the receiver which is substantially ofthe same quality as that produced by the'induced phone circuit.

The current controlling and switching apparatus B consists in a variable resistance 1 s nut 10 and switches 7 and 11. The resistance elements of the shunt 10 are bridged across the conductors 16 which are connected winding of the vibrator 1. Intermediate etween the points where the resistance elements are bridged across the circuit and the secondary winding of the vibrator, current limiting resistance R, and R are in circuit. Oneside of said circuit is connected with the middle backcontact of switch 7, and the movable arm of shunt current in the tele- 10 is connected with the left hand back contact of switch 7. Current limiting resistances R and R are inserted between the point where said shunt is bridged across the circuit and switch 7. Resistances R R R and R, are large compared with the variable resistance 10 and the impedance of the circuit containing said resistances, looked at from the direction of the arrow X is substantially the same for all settings of the variable resistance 10, in consequence whereof the current output of the secondary winding and the frequency and tone of the vibrator remain substantially the same throughout the entire range of the variable resistance 10. The right hand back contact and the right hand swinging contact of switch 7 are connected by conductors 12 with the primary winding of vibrator 1 in order to close the circuit through the primary windin and thereby start the vibrator to operate w enever switch 7 is closed. A receiver D is connected by means of conductors attached to binding posts 13 and with the corresponding contacts of switch 11. The telephone circuit C which has an alternating current induced in it is connected through binding posts 14 and 14 to the left hand and middle swinging contacts of the switch 11.

If it is desired to make a test across the two wires of the pair, a resistance R the magnitude of which depends upon the electrical characteristics of the circuit C, is bridged across the end of the circuit farthest removed from the point at which the test is being made. If it is desired, on the other hand, to measure the current between the circuit and ground, the distant end of the circuit is grounded as shown by the dotted lines of the circuit C. A current limiting resistance R, is arranged so as to be connected in series with the receiver D whenever a measurement to ground is being made. The right hand back contact of switch 11 is grounded so that whenever said switch is operated contact 15 is closed, thus ground ing one side of. receiver D which is necessary for making the grounded circuit test.

Having in mind this description of the parts of this apparatus, and of the function that each part performs, the method of making a measurement of the magnitude of induced current on 'a telephone line may be readily understood. If it is desired to make a test on the circuit C, the said circuit is connected as shown to binding posts 14: and 14, the receiver D is connected to binding posts 13 and 13 and the tone standard A is connected with the current controlling and switching apparatus B by means of conductors 12 and 16. With the switches 7 and 11 in their normal positions the receiver D is bridged across the two sides of circuit C and an observer listens and notes the magnitude of the tone. Then switch 7 is operated disconnecting the receiver from the circuit and connecting it with the tone source A. If the tone therefrom is found to be greater than that produced by the circuit, the shunt 10 is adjusted so as to decrease it. The receiver is alternately bridged across the circuit and the tone source, and the shunt is varied until the volume of tone created by the circuit and by the tone source is substantially the same. It will be seen that by controlling the flow of current through the primary circuit of the vibrator by means of the right hand contacts of switch 7, the vibrator operates only when the receiver is bridged across the tone source, which increases the life of the batteries, and thereby renders it possible to'maintain the tone uniform during a considerable period of time.

If it is desired to make a measurement between the telephone circuit and ground, the circuit is arranged as indicated by C, and switch 11 is operated, which sets up a circuit from ground through contact 15 and conductor 17, receiver D, resistance R through the two wires in parallel of circuit C to ground. After noting the magnitude of the tone in the receiver D, switch 7 is operated and a comparison is made with the tone from the tone source A. By alternately connecting the receiver with said source and said circuit, and operating theshunt 10 in the same manner in which it is operated when makin the metallic circuit test, a balance is de nitely reached between the tones created in the receiver. The shunt 10 is calibrated so as to indicate the number of units of current sent through the receiver D.

It will be readily seen that by means of this apparatus which is sufficiently small to be readily transported, measurement may be made in the field by persons who are relatively unskilled in electrical testing, and greater accuracy is attainable than was heretofore practicable with the apparatus then known in the art.

Although the invention has been disclosed as embodied in a particular form, it is evident that it is not restricted to such form, that it may be embodied in a variety of different forms without departing from the spirit and the scope of the claims herewith.

What is claimed is:

1. In electrical measuring apparatus, the

, therein an alternating current, a

' combination of a source of alternating current, controlling means therefor, a circuit having induced therein an alternating current, indicating means, and switching means whereby said indicating means may be alternately connected with said source and said circuit.

2. In electrical measuring apparatus, the combination of a source of alternating current, a circuit having induced therein an alternating current, indicating means, switching means to connect said indicating means with either said source or said cir cuit, and a shunt across said source whereby the current from said source to said indicating means may be varied.

3. In electrical measuring apparatus, ,the combination of a source of alternating current, a second source of alternating current, indicating means, switching means to connect said indicating means alternately with said first and said second source, and means to substantially equalize the magnitude of the signal given by said indicating means.

4. In electrical measuring apparatus, the combination of a source of alternating current, a circuit having induced therein an alternating current, indicating means, switching means to connect said indicating means alternately with saidsource of said circuit, and to render said source operative only when connected with said indicating means.

5. In electrical measuring apparatus, the combination of a circuit havin induced buzzer designed to produce an alternating current the wave form of which simulates that of the current induced in said telephone circuit, a telephone receiver, and means to connect said receiver alternately with said circuit and said buzzer, and a variable shunt whereby the magnitude of current transmitted from said buzzer to said receiver may be varied until the tones given by said receiver when connected with said circuit and with said buzzer are substantially equalized.

6. In electrical measuring apparatus, the combination of a buzzer having an output circuit, a pair of conductors having an impedance coil bridged across one end, indicating means and switching means adapted to bridge said indicating means alternately across said output circuit and other end of said conductors.

7. In electrical measuring apparatus, the combination of a buzzer having an output circuit, a pair of conductors having one end short circuited and grounded, indicating means and switching means adapted to connect said indicating means alternately with said output circuit and with said conductors and a second switching means adapted to short circuit the other end of said conductors and to connect in series therewith an impedance coil and to ground one side of said indicating means.

In testimony whereof, I have signed my name to this specification this 8th day of August 1918.

MAGLEAN KIRKwoon. 

